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unilide is known in pharmacy as antifebrin, and is used as an
ni-Dinitrobenzene. In the Notes on Prep. 48, p. 274,
it is mentioned that the second nitro-group enters the meta-
position to the first. This is usually the case where two
acid groups arc successively introduced into the hydrocarbon.
Thus, ben/enedisulphonic acid, obtained by heating benzene
sulphonic acid (see Prep. 74, p. 177) with fuming sulphuric acid,
is a meta-compound.
m-Nitraiiiline.—The reduction product of w-dinitrobenz-
ene is naturally ///-nitranilinc. The o- and /-nitranilines can
be obtained by acting upon aniline or, preferably, acetanilide,
with fuming nitric acid.
Whereas the first nitro-group of a tri- or di-nitro derivatives is
rapidly and completely reduced by ammonium sulphide, the
second is very slowly attacked. The rate of change appears to
he determincd mainly by the acidic nature of the molecule as a
whole, the halogens and carboxyl playing a similar role to that of
the nitro-group. In all these cases hydroxylamine compounds
are produced as intermediate products.
Dimethylamline.-......It is a well-known Yfact that the alkyl
halidcs convert the primary amines into secondary and tertiary
bases (Ilofmann). The formation of dimethylaniline is prob-
ably due to the action of CH;1C1, which is formed, as an
intermediate product, by the action of hydrochloric acid on the
methyl alcohol. There is always a small quantity of mono-
methylaniline, C,.Hf>NIICH:l, produced at the same time. The
three bases cannot well be separated by fractional distillation,
as their boiling points lie too near together,
Aniline      ..........180°.
It is for this reason that the action of acetic anhydride is
utilised, which only unites with the primary and secondary base.
Dimethylaniline is a weak base, which, like aniline, is neutral